"Apple was ranked last because of its failure to make any progress in
its recycling and toxic content policies, Greenpeace said in its report. The environmental group started publishing the list
in August 2006. Apple also was taken to task by Greenpeace for failing
to release the full list of regulated substances it uses, and for
refusing to provide timelines for eliminating use of the most toxic
substances.

In addition, Apple "performs poorly" in product take-back and
recycling, Greenpeace said. The only positive for Apple is that it
reports on the amounts of its electronic waste recycled."

As might be expected, Apple wasn't accepting the low ranking without a bit of a challenge:

"Apple took issue with Greenpeace's ranking system. "We disagree
with Greenpeace's rating and the criteria they chose," a company
spokeswoman said. "Apple has a strong environmental track record, and
has led the industry in restricting and banning toxic substances, such
as mercury, cadmium, and hexavalent chromium, as well as any BFRs.